For the centrifugal treatment of such fluids it is known to use cyclone-type separators in which the fluid is axially and tangentially guided through a centrifugation chamber with widely varying radii of curvature. The desired rotary and axial motion is imparted to the fluid stream by vanes or baffles at one axial end of the chamber, the fluid swirling then under its own momentum toward the opposite end. This mode of vortex generation results in complex flow conditions with superimposition of secondary currents and large losses of energy due to collisions and friction along the walls.